Flagging

Flagging is the practice of wearing specific clothing, insignia, or
accessories to indicate a particular BDSM or sexual interest or orientation.

In the Leather Subculture, the Hanky Code provides
a way of declaring interests using different coloured handkerchiefs worn
in a back trouser pocket (eg gray = bondage). Although the use of
flagging has declined, it is conventional for tops to wear the hanky on
the left,
and bottoms to wear it on the right. This convention may also extend to
keys.

There is no universal flagging convention in O&P, but due to the large
overlap with the M/s tradition within Leather, the same
left-right associations would be an obvious choice.

The collar worn by owned submissives and slaves can
also be seen as a form of flagging, and the
Ownership Icons provide a set of visual flags.

The iron signet ring in the Story of O can be
viewed as a fictional instance of flagging.